Hi,
I have a big dilemna on one machine :
I run a task with RT priority which make a loop to mesure the system
perturbation.
It works well except on one machine.
On a multi-cpu, If I run the program on cpu 1, I get 23us. It's OK.
If I run the same program on cpu 0, I get 17373us !
If I do :
# echo 0 >/proc/sys/kernel/preempt_max_latency
# ./tsc 0
temps deb 60229d5e6ee
cptr mlockall 0
temps fin 6c386df6612
temps max 1 6472c52d682
temps max 2 6472fa35c26
duree du test 259.450819 s max detecte 17373 µs
#cat /proc/latency_trace
preemption latency trace v1.1.4 on 2.6.12-RT-V0.7.51-13-DAV06
--------------------------------------------------------------------
latency: 33 us, #48/48, CPU#1 | (M:rt VP:0, KP:1, SP:1 HP:1 #P:2)
-----------------
| task: softirq-timer/1-12 (uid:0 nice:-10 policy:0 rt_prio:0)
-----------------
_------=> CPU#
/ _-----=> irqs-off
| / _----=> need-resched
|| / _---=> hardirq/softirq
||| / _--=> preempt-depth
|||| /
||||| delay
cmd pid ||||| time | caller
\ / ||||| \ | /
<idle>-0 1Dnh3 0us!: <70617773> (<00726570>)
<idle>-0 1Dnh3 0us : __trace_start_sched_wakeup (try_to_wake_up)
<idle>-0 1Dnh3 0us : __trace_start_sched_wakeup <<...>-12>(69 1)
<idle>-0 1Dnh3 0us : _raw_spin_unlock (try_to_wake_up)
<idle>-0 1Dnh2 0us : resched_task (try_to_wake_up)
<idle>-0 1Dnh2 0us+: try_to_wake_up <<...>-12> (69 8c)
<idle>-0 1Dnh2 22us : _raw_spin_unlock_irqrestore
(try_to_wake_up)
<idle>-0 1Dnh1 22us : preempt_schedule (try_to_wake_up)
<idle>-0 1Dnh1 22us : wake_up_process (trigger_softirqs)
<idle>-0 1Dnh. 23us : preempt_schedule_irq (need_resched)
<idle>-0 1Dnh. 23us : __schedule (preempt_schedule_irq)
<idle>-0 1Dnh. 23us : profile_hit (__schedule)
<idle>-0 1Dnh1 23us : sched_clock (__schedule)
<idle>-0 1Dnh1 23us : _raw_spin_lock_irq (__schedule)
<idle>-0 1Dnh1 24us : _raw_spin_lock_irqsave (__schedule)
<idle>-0 1Dnh2 24us : pull_rt_tasks (__schedule)
<idle>-0 1Dnh2 24us : double_lock_balance (pull_rt_tasks)
<idle>-0 1Dnh2 24us : _raw_spin_trylock (double_lock_balance)
<idle>-0 1Dnh3 25us : pick_rt_task (pull_rt_tasks)
<idle>-0 1Dnh3 25us : find_next_bit (pick_rt_task)
<idle>-0 1Dnh3 25us : find_next_bit (pick_rt_task)
<idle>-0 1Dnh3 25us : find_next_bit (pick_rt_task)
<idle>-0 1Dnh3 25us : _raw_spin_unlock (pull_rt_tasks)
<idle>-0 1Dnh2 26us : preempt_schedule (pull_rt_tasks)
<idle>-0 1Dnh2 26us : find_next_bit (pull_rt_tasks)
<idle>-0 1Dnh2 26us : find_next_bit (pull_rt_tasks)
<idle>-0 1Dnh2 26us : dependent_sleeper (__schedule)
<idle>-0 1Dnh2 26us : _raw_spin_unlock (dependent_sleeper)
<idle>-0 1Dnh1 27us : preempt_schedule (dependent_sleeper)
<idle>-0 1Dnh1 27us : _raw_spin_lock (dependent_sleeper)
<idle>-0 1Dnh2 27us : find_next_bit (dependent_sleeper)
<idle>-0 1Dnh2 27us : dequeue_task (__schedule)
<idle>-0 1Dnh2 27us : recalc_task_prio (__schedule)
<idle>-0 1Dnh2 28us : effective_prio (recalc_task_prio)
<idle>-0 1Dnh2 28us : enqueue_task (__schedule)
<idle>-0 1Dnh2 28us : trace_array (__schedule)
<idle>-0 1Dnh2 29us : trace_array <<...>-12> (69 6e)
<idle>-0 1Dnh2 29us : trace_array (__schedule)
<...>-12 1Dnh2 31us : __switch_to (__schedule)
<...>-12 1Dnh2 31us : __schedule <<idle>-0> (8c 69)
<...>-12 1Dnh2 31us : finish_task_switch (__schedule)
<...>-12 1Dnh2 31us : _raw_spin_unlock (finish_task_switch)
<...>-12 1Dnh1 32us : trace_stop_sched_switched
(finish_task_switch)
<...>-12 1Dnh1 32us : _raw_spin_lock (trace_stop_sched_switched)
<...>-12 1Dnh2 32us : trace_stop_sched_switched <<...>-12>(69 1)
<...>-12 1Dnh2 32us : trace_stop_sched_switched
(finish_task_switch)
vim:ft=help
My Question is : where is the time missing ?
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